Line tangent to the curve

  • Thread starter mbisCool
  • Start date
  • #1
135
0

Homework Statement



For what values of a and b is the line 3x+y=b tangent to the curve y=ax^3 when x=5 ?


The Attempt at a Solution


I believe i would need to find the equation of the tangent to y=ax^3 when x=5 then that should be equal to -3x+b=y if im not mistaken but im not sure what to do from here to solve for a and b.

Any leads in the right direction or insight if this is the entirely wrong approach would be greatly appreciated!
 

Answers and Replies

  • #2
HallsofIvy
Science Advisor
Homework Helper
41,833
964
I believe i would need to find the equation of the tangent to y=ax^3 when x=5 then that should be equal to -3x+b=y if im not mistaken
Well, yes, that's just a restatement of the problem! You know that the slope of y= -3x+ b is -3. What connection is there between the slope of a tangent line and the function itself?
 
  • #3
135
0
thank you for the quick reply hallsofivy. I had -0.04 instead of -3/75 giving me the wrong answer for the online homework webpage which was confusing me. After using -3/75 instead it counts it as correct :(
 

Related Threads on Line tangent to the curve

  • Last Post
Replies
3
Views
984
  • Last Post
Replies
1
Views
9K
  • Last Post
Replies
2
Views
5K
Replies
9
Views
31K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
4
Views
1K
Replies
4
Views
5K
  • Last Post
Replies
3
Views
4K
  • Last Post
Replies
3
Views
953
Replies
5
Views
3K
Top